In any mine with underground excavations there is a risk of collapse. Wieliczka is no exception. Headings had to be secured and weak spots supported.
In addition to leaving natural pillars of salt, timber cribs and linings were constructed between floor and ceiling. Salt, as we know, is a great preservative, and the wood remains undecayed over the centuries. But the structures themselves, being subjected to enormous pressures from the surrounding rock, eventually show signs of fatigue.
The combination of timber and tallow candles in the mine was of course unpropitious, and several serious fires have been recorded. When cribs and linings burned there was always a danger of subsidence, and many buildings in the town were wrecked and even engulfed by the mine.
Apart from fire, there was the ever-present risk of explosion from methane gas, which exuded from newly excavated rock masses and collected under the ceilings of poorly ventilated chambers. The unenviable task of burning out these pockets of gas was performed by so-called "penitents" creeping on hands and knees, carrying lighted torches on long poles.
But the greatest enemy of salt is water, and the influx of water into the mine, both as minor seepages and as large-scale flooding, has always presented a serious problem. A bad flood in 1992 was a sharp reminder of this ever-present threat.